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From the Early Triassic Wordie Creek Formation of East Greenland

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From the Early Triassic Wordie Creek Formation of East Greenland Remains of Saurichthys (Pisces, Actinopterygii) from the Early Triassic Wordie Creek Formation of East Greenland ILJA KOGAN Kogan, I. 2011. Remains of Saurichthys (Pisces, Actinopterygii) from the Early Triassic Wordie Creek Formation of East Greenland © 2011 by Bulletin of the Geological Society of Denmark, Vol. 59, pp. 93–100. ISSN 0011–6297. (www.2dgf.dk/publikationer/bulletin) https://doi.org/10.37570/bgsd-2011-59-09 Previously undescribed specimens of Saurichthys from the basal part of the Early Triassic Wordie Creek Formation (Griesbachian) of East Greenland demonstrate a remarkably complete squamation especially in the anterior trunk portion. Scales of the mid-lateral row are high and those of the mid- dorsal and mid-ventral rows broad and conspicuous by having a pronounced longitudinal keel on their inner surface; additional dorso-lateral and ventro-lateral scale rows are present. This pattern resembles that of Saurichthys dayi from the Early Triassic of Alberta and British Columbia. Differences in fin morphology suggest, however, that the Greenland form is probably not conspecific. A second Early Triassic species of Saurichthys occurring in East Greenland probably comes from a higher stratigraphic level (late Griesbachian to early Dienerian) with a different ichthyofaunal composition. Received 28 July 2011 Accepted in revised form 11 November 2011 Key words: Saurichthys, East Greenland, Wordie Creek Formation, stratigraphy. Published online 2 December 2011 I. Kogan [[email protected]], Freiberg University of Mining and Technology, Geological Institute, Bernhard- von-Cotta str. 2, 09599 Freiberg, Germany. Numerous fossil fishes from the Early Triassic of East Material and methods Greenland have been collected in the course of several Danish palaeontological expeditions in the 1930s. First The three specimens described below have been col- remains of Saurichthys Agassiz, 1834 were discovered lected by E. Nielsen during the 1930s in the Kap Stosch by Eigil Nielsen in 1932 and only briefly mentioned in area at the north coast of Hold with Hope, East Green- his subsequent publications (Nielsen 1935, 1936, 1961). land (Fig. 1). Nielsen (1935) distinguished six subsequent The fourteen specimens reported in Nielsen (1961) are vertebrate-bearing levels, i.e. five “fish zones” and one stored in The Natural History Museum of Denmark, “tetrapod zone”, in his study area. Of the 14 Saurichthys Copenhagen (Geological Museum – MGUH numbers) specimens enumerated in Nielsen (1961), five were and have never been described in detail, except for referred to his fish zone 2 and nine to his fish zone 5. two skulls (MGUH-VP-992 and -994) that were pub- According to the labels, specimens MGUH-VP-1000 and lished by Mutter et al. (2008) who referred to them as -997 were found in 1933 at the so-called Østlokaliteten Saurichthys cf. ornatus. and Vestlokaliteten, respectively. These localities are Already Nielsen (1936) suggested the possible mentioned in Nielsen (1935: fig. 19) and belong to his fish presence of more than one saurichthyid species in his zone 2 (Nielsen 1935: 100 ff.). Both localities are situated collection because of differences in size and propor- in the Neviatiakdal area and placed in the former Otocer- tions. A preliminary survey of the material indicates as beds. This level corresponds to the interval from that the occurrence of different morphotypes prob- Hypophiceras martini to Metophiceras subdemissum zone ably corresponds to two distinct stratigraphic levels. (lowermost upper Griesbachian) in the stratigraphic At least the specimens MGUH-VP-988, -997 and -1000 scheme of Bjerager et al. (2006) and occurs near the base are referable to a single morphotype based on their of the Wordie Creek Formation only few metres above peculiar squamation. They are described in the fol- the presumed Permian-Triassic boundary. No detailed lowing account. information is given on the specimen MGUH-VP-988. Remains of Saurichthys (Pisces, Actinopterygii) from the Early Triassic Wordie Creek Formation · 93 All specimens are preserved as concretions in laminated Systematic palaeontology mudstones deposited under marine conditions during a period of local sea-level rise (Bjerager et al. 2006). Subclass: Actinopterygii Cope, 1887 The fossils were studied under a WILD binocular Order: Saurichthyiformes Aldinger, 1937 microscope and photographed with a NIKON D 80 Family: Saurichthyidae Owen, 1860 digital camera with a 35-70 mm zoom lens. Drawings [sensu Stensiö 1925] were made by means of a camera lucida as well as on Genus: Saurichthys Agassiz, 1834 the basis of photographs. To enhance contrasts, speci- Type species: Saurichthys apicalis Agassiz, 1834 men MGUH-VP-988 B was examined and photographed immersed in alcohol. Saurichthys aff. dayi (Raymond, 1925) The use of open nomenclature follows Bengston (1988). Referred material: MGUH-VP-1000 (anterior trunk portion and incomplete skull), MGUH-VP-997 (trunk fragment), MGUH-VP-988 A, B (trunk fragment with dorsal and anal fins in part and counterpart); possibly also MGUH-VP-990 (fragmentary skull) and MGUH- VP-996 (caudal peduncle). Description Specimen MGUH-VP-1000 (Fig. 2) is an incomplete skull with the anterior body portion preserved in a concretion. Most dermal bones of the skull are weath- ered away and only the right mandible and the right opercular are preserved in lateral view. The preserved portion of the mandible is 124 mm long and the tip of the snout is missing. Delicate subvertical striae can be recognized on the dentary. Some teeth are preserved on both jaws, the largest of them being ca. 4 mm high by 2.5 mm wide. The opercular is considerably higher than long (28 mm high, 17 mm long) and ornamented with con- centric ridges of ganoin parallel to its margins. The cleithrum has the shape of an inverted ‘T’ whose ante- rior and posterior branches are nearly equal in length. The pectoral fin is fan-shaped and consists of at least 18 unsegmented lepidotrichia. The postcranial body fragment shows 18 mid-lateral scales. They are very high (ca. 25 mm in height to 5 mm in length along the lateral line) and roughly rec- tangular in shape, and the lateral line sensory canal divides them into a somewhat smaller upper (dorsal) part and a larger lower (ventral) part. The scales are inclined anteroventrally and ornamented with a combination of ridges and tubercles of ganoin. In the lower parts, subvertical and somewhat sigmoidal ridges predominate and tubercles are restricted to the margins of the scale. The pattern is similar in the up- per parts of the anteriormost scales, whereas farther back the ornament is composed of tubercles arranged Fig. 1. Map of East Greenland showing the outcrop areas of the in subhorizontal rows. Early Triassic Wordie Creek Formation and the assumed find Further scales are present on the body but neither locality of Saurichthys aff. dayi on the north coast of Hold With their number nor their exact shape can be determined Hope. Modified from Bjerager et al. (2006). due to the preservation. It seems, however, that the 94 · Bulletin of the Geological Society of Denmark anterior scales of the mid-dorsal row are oval and very mid-lateral scales. The ornamentation is composed of small, increasing in size posteriorly. tubercles arranged in longitudinal rows. Specimen MGUH-VP-997 (Fig. 3) represents a cast The portion dorsally to the mid-lateral scales is in- of a body fragment presumably between the skull and sufficiently preserved. Several scales of different size the pelvic fins. Remnants of 8 mid-lateral scales are are present, which could possibly reflect the pattern visible. They show the same proportions as described in the ventral part. for specimen MGUH-VP-1000, but it can be seen that Specimen MGUH-VP-988 A and B (Fig. 4) repre- the sigmoidal subvertical ridges that constitute the sents the region of the dorsal and anal fin in part and ornamentation of their lower parts are mainly com- counterpart. About 20 mid-lateral scales are preserved posed of fused tubercles. The upper parts of the scales anteriorly to the fins; compared to the mid-lateral are ornamented with distinct tubercles arranged in scales of more anterior body segments, documented curved, subhorizontal rows. by specimens MGUH-VP-1000 and -997 (apparently Three rows of scales can be distinguished between belonging to individuals of comparable size) they are the mid-lateral and the mid-ventral scale row. The less high (about 20 mm) and slightly more rhombic scales correspond to the mid-lateral scales in number. than rectangular in outline. Their length, however, The long axis of all of these ventrolateral scales is is still between 4 and 5 mm, and the ornamentation anteroventrally directed, opposing the anterodorsal follows the pattern described above. Comparatively axis of the mid-lateral scales. Scales of the uppermost larger areas of the lower part of the scales, near their ventrolateral row are bigger and rectangular in shape anterior and ventral margins, are covered with tu- (ca. 8 to 4 mm), the remaining scales are 3-5 mm long bercles. The scales of the mid-dorsal and mid-ventral and oval to triangular. All of them are ornamented rows are only half as numerous as the mid-lateral ones; with tubercles. further scale rows seem not to be present. The mid-ventral scales are preserved only as im- Scales of the mid-ventral and mid-dorsal rows have pressions of their outside. They are cordiform to V- the same shape in front of the dorsal and anal fins. shaped, pointing posteriorly, 5 mm wide and 7 mm They are rounded, 10-11 mm broad and 11-12 mm long. long. They also roughly correspond in number to the On the inside, a prominent longitudinal keel runs Fig. 2. Saurichthys aff. dayi, incomplete skull and anterior body portion. Specimen MGUH-VP-1000. Remains of Saurichthys (Pisces, Actinopterygii) from the Early Triassic Wordie Creek Formation · 95 along the midline, passing from one scale to another.
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